Accurate tracking of moving objects within monitored scenes is crucial to a range of surveillance tasks. There are many effective methods of detecting and tracking objects, and many analyzes have been conducted to improve object tracking technique accuracy. Techniques used in object tracking are categorized on the basis of the type of tracked objects and the type of motion representations. A significant challenge in video object tracking is occlusion, i.e. a situation when the tracked object is covered by other objects. During occlusion, ambiguities concerning occluded object features occur frequently.
In real life situations, three types of occlusions occur: (A) self-occlusion when one part of the object occludes another, (B) inter-object occlusion when one object being tracked occludes another object and (C) occlusion by the background when a structure from the background occludes the tracked objects.
A U.S. Pat. No. 6,542,621 discloses a method of dealing with occlusion when tracking multiple objects and people in video sequences, that employs probabilistic templates, or p-templates, which probabilistically encode the rough position and extent of the tracked object's image. The p-templates track objects in the scene, one p-template per object. They can be used to incorporate three-dimensional knowledge about the scene, and to reason about occlusion between the objects tracked by the p-templates. This requires video capture and digitization hardware, image processing hardware such as a digital signal processor, and a method for estimating the image size of a person standing at a given location in the image.
A U.S. Pat. No. 8,086,036 discloses an approach for resolving occlusions, splits and merges in video images, which provides an environment in which portions of a video image in which occlusions have occurred may be determined and analyzed to determine the type of occlusion. Furthermore, regions of the video image may be analyzed to determine to which region the object in the occlusion belongs to. The determinations and analysis may use such factors as pre-determined attributes of an object, such as color or texture of the object and/or a temporal association of the object, among others.
It would be advantageous to provide a method for video object tracking, which could handle object occlusions in an effective manner.